Yammer’s biggest rule of thumb is “2 to 10 people, 2 to 10 weeks,” ... If you employ the “2 to 10″ rule, it’ll also force you to release often, test your assumptions, and not over-invest in mistakes.

and

While everybody knows how expensive context switching is, it’s staggering that nobody builds that into their organization as a constraint. With total focus, you build one thing, ship it, and then are able to move onto something else.